Means for and method of secret signaling



Aug. 6, 1946. G. GUANELLA 2,405,500

MEANS FOR AND METHOD OF SECRET SIGNALING Filed Feb. 26, 1944 2 Sheets-sheaf. 1

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HTTORNEY Aug. 1946.

G. GUANELLA MEANS FOR AND METHOD OF SECRET SIGNALING Filed Feb. 26, 1944 2 Sheets-Sheet 2 4 7 mm 2 m a "m mm 6 J W Z w 6 Y B G iimm H- ELM w w. H "m -n flTTORNEY Patented Aug. 6, 1946 MEAN S FOR AND METHOD OF SECRET SIGNALING Gustav Guanella, Zurich, Switzerland, assignor to Radio Patents Corporation, New York, N. Y., a corporation of New York Application February 26, 1944, Serial No. 524,079

In Switzerland January 29, 1942 20 Claims. (01. 1791.5) 1 2 The present invention relates to means for and The disadvantages inherent in the known a method of secretly transmitting speech or like scrambling arrangements are substantially messages by scrambling the signals at the transmitting end and unscrambling them at the receiver, and a major object of the invention is to provide an improved and simplified system of this type which principally eliminates the necessity of using synchronously moving devices at the receiver and transmitter required with known secrecy transmission systems, while at the same time affording an increased degree of secrecy and substantially preventing any possibility of deciphering the signals by an unauthorized receiver.

According to known methods of scrambling speech or like messages, the components of the message to be scrambled are shifted in frequency by predetermined amounts before transmission and then shifted back again by corresponding amounts at the receiving end. This frequency substitution is eiiected by modulation with certain control signals at the transmitting and the receiving end. With other known methods, the amplitude of individual signal frequency subbands is varied in accordance with the control signals. All methods of this type, where the message to be scrambled is modulated by a control signal are able to guarantee an adequate degree of secrecy only if the control signals are variable, since otherwise an unauthorized receiver who succeeds in unscrambling a short section of the message would have knowledge of the constant control signal and thus be in a position to unscramble the entire message without difliculty.

For this reason, scrambling and unscrambling are often varied in accordance with a, prearranged program or schedule. The control signals are produced in the transmitter and also in the receiver by means of devices which must be maintained in exact synchronism so that the control signal at the transmitting end equals at any instant the control signal at the receiving end to enable an intelligible message to be reproduced.

A disadvantage of these known arrangements is due to the fact that it is difficult in many cases to maintain the synchronism between the transmitting and receiving devices. Synchronizing impulses may be transmitted to ether with the scrambled message in order to effect a continuous control of the synchronizing process. There are,

however, considerable difficulties to be overcome in practice to maintain synchronous operation, not to mention the elaborate equipment required and the cost thereof.

control signals used for avoided by the present invention by transmitting a variable control signal from the transmitter to the receiver from which control signal at least one scrambling signal is obtained both at the transmitter and at the receiver by converting it in accordance with an adjustable key. The scrambling signal thus obtained is utilized to effect scrambling of the message at the transmitter and its unscrambling at the receiver in accordance with any one of the scrambling arrangements and methods known in the art.

By such a method, a special synchronization of the transmitting and receiving devices becomes superfluous and a high degree of secrecy is obtained with relatively simple means.

The invention will be further understood from the following detailed description taken in reference to the accompanying drawings forming part of this specification and wherein:

Figure 1 is a block diagram showing a basic secret signaling system embodying the principles of the invention;

Figures 2 and 3 are diagrams similar to Figure 1 showing modifications of the invention;

Figure 4 is a block diagram showing in more elaborate manner a complete transmitting and receiving system for secret transmission of speech or like messages according to the invention;

Figure 5 illustrates a modification of another practical speech scrambling arrangement according to the invention;

Figure 6 is a theoretical diagram explanatory of the function and operation of Figure 5; and

Figure 7 is a detailed diagram showing one way of producing a complex periodic scrambling and unscrambling signal for use in connection with the invention.

Like reference characters identify like parts throughout the difierent views of the drawings.

Referring more particularly to Figure 1, there is shown a transmitter S and a receiver E of a secret signaling system according to the invention. The signals at which are to be scrambled such as electric speech oscillations are modulated in the modulating device M with the scrambling signal '0, so that an unintelligible signal a is obtained which is transmitted to the receiver E. Transmission may be effected in any known manner either directly or in the form of a modulated carrier current. By means of a further modulation of the scrambled signals with the unscrambling signal 10 in the receiver E the original signal a: is again obtained,

It is advantageous to employ the frequency of control signal it as its characteristic feature, in which case it is possible to alter the control frequency in accordance with any desired program without influence by the characteristics of the transmission channel. The control signal it and the scrambled signal 2 may be transmitted over the same conductor if different frequency channels are provided for both signals; As is understood, the direction of transmission can be reversed, in which case the transmitter becomes the receiver.

As pointed out, the control signal a may be derived from the energy of the unscrambled si nal w to be transmitted, in which case the generator G is replaced by a suitable converter U, as

shown in Figure 2. The output of the converter then supplies the control signal it serving for controlling the scrambling of the message being transmitted.

It is furthermore possible, as shown in Figure 3, to derive the control signal it both at the transmitter and receiver from the scrambled signal 5 with the aid of the network U, in which case only one channel will be required for the transmission. The 7 control signal frequency range may comprise the range of the total range of signal 2 or may comprise a certain'frequency portion or sub-band of the signal a.

In all the above cases, it is a signal whose amplitude and/or frequency is irregularly variable. Since this signal may be picked up by an unauthorized receiver, the conversion in the devices V and W should be such as not to be easily determinable so that an unauthorized receiver may not be able to reproduce the correct unscrambling signal w required for unscrambling the message.

The scrambling of the message at the transmitting end and its unscrambling at the receiving end by means of the signals 0 and w is effected by the devices M and N, respectively. For this purpose, any known method such as amplitude control, frequency shifting or "substitution or time-controlled transmission of the signals may be employed. Thus, scrambling and unscrambling of the message by means of .the; ignals u and 'u may occur by a frequency shift in accordance with the momentary scrambling frequency or by an amplitude control of the message frequency band or sub-bands thereof.

Alternatively, the message may be transmitted over a'network with frequency-dependent transmission characteristic, the tuning of which is influenced by the scrambling or unscrambling signals, respectively. In order to achieve a, higher degree of secrecy, the message may first of all be divided into at least two frequency sub-bands each of which is subjected to an amplitude and/ or frequency modulation in accordance with the scrambling signals. In this manner, the individual frequencies of which a, message such as a speech band is composed may be thoroughly 4 an endless magnetic record such as a steel tape whose traveling speed is varied according to the scrambling signals.

In Figure 4 there is shown by way of example an arrangement wherein th signal as to be scrambled is divided by means of a plurality of band pass filters, four such filters F1, F2, F3, F4 being shown in the drawings, into frequency sub-bands an, 322, ms, :174 whose amplitude is varied in the modulators M1, M2, M3, M4 in accordance with the scrambling voltages v1, v2, '53, v4, sothat the speech or message e upon recombination of the sub-bands becomes unintelligible.

The variable amplitude and/or frequency of the control signal may be utilized to produce the scrambling signals v1, v2, v3, and m. In order to obtain a relation between the control and scrambling signals which cannot be easily discovered, it is advisable to use retardation means having adjustable retardation times or filters with adjustable tuning and dam-ping. signals may be further converted by frequency The control multiplication or division, by the formation of modulation products or by influencing special scrambling voltage generators by means of the scrambling signals. In the arrangement shown in Figure 4, the scrambling signal voltages are obtained by filtering four optional frequency bands from the control signal u which, as pointedout, may be supplied .by a special generator G or derived from the .unscrambled signal m. For this purpose, the signal it is passed through four electrical filters H1, H2, H3, H4 with unequal and preferably variable tuning and damping adjustment and then rectified in rectifiers D1, D2, D3, D4. Ina simplified form of thisqarrangement, the networks -1 maybe constructed as simple bandpass filters, whereby the various scrambling signals will only be dependent on the average amplitude of the partial voltages or sub-bands of the control signal passing through the corresponding filters.

It is furthermore possible to render. at least one scrambling signal dependent on the frequency of the control signal by the use of frequency modulation or when complex control signals are used to render the scrambling signals dependent 0n the various frequencies of the control signal.

A similar arrangement is provided at the receiving end for cancelling or compensating the amplitude variations of the individual signal freto the filters H1, H2, H3, H4 and rectifiers D1, D2,

D3, D4, respectively, at the transmitter and serve to produce control signal components in, us, us and 11.4 and unscrambling signal components 101, w, ws andwi. The receiving modulators N1, N2, N3, N4 should, however, be controlled in the opposite sense to the modulators M1, M2, M3, M4 at the transmitting end, in order to obtain the original clear speech signals-m.

Another arrangement for carrying out the invention is shown in Figures 5 and 6. By separately modulating the message a with the auxiliary frequencies s1 and $2 in the modulators K1 and K2 and filtering out one side band by means of filters B1 and B2, the transposed speech frequency bands 01 and-c2 are obtained. These intermediate frequencies are again modulated in the scrambling modulator M with the "variable scrambling frequency c, which may be'varied-between the value 1; and o" so as to Obtain the sum and difference frequencies of the signal bands 01 or 02, respectively, nd the scrambling frequency v. The frequency band e whose width is equal to that of the original band a is segregated from the resulting modulation product by means of the band pass filter B3 and, after a further modulation in K3 with a frequency w, is shifted back into the original speech frequency range Z.

The scrambled signal 2 thus formed contains all the original message components with a different frequency as shown in Figure 6. In the latter, the position of the frequencies of the individual bands is indicated by shaded rectangles and the beating oscillator frequencies are indicated by arrows. The original message a: is represented by the rectangle a. By modulation in K1 and K2 the transposed sum and diiierence frequency bands b1, 01 obtained of which the by means of the band pass filters B1 and B2.

bands 01, 02 are segregated y modulation with the variable control frequency 12 having a momentary value of 6000 c./sec. in the example illustrated, the sum frequency bands di and d2 are formed. Band e passing through filter B3 is finally modulated in K3 with the frequency w and the sum frequency band of the modulation product suppressed by the filter B4. The remaining difference frequencies constitute the scrambled signal 2 which contains all components of the original message a: with a frequency shift determined by the momentary frequency of the control signal 12. The originally lowest message frequency of 200 c./sec. is thus displaced by varying amounts and is now immediately next to the originally highest message frequency of 2500 c./sec. The distance of the diagonals shown in the rectangles from the corresponding abscissae represents the magnitude of the frequency components and also shows at which point of the frequency scale said components have been displaced by the modulation.

In order to produce the scrambling signal '0 from the control signal u, an arrangement with 1 adjustable retarding devices C1, C2 and C3 in the form of rotating steel tape may be employed as shown in greater detail in Figure 7. Devices C1, C2 and C3 comprise in a known manner adjustable recording magnets A1, A2, A3, reproducing magnets A4, A5, A6 and quenching magnets A7, A8, A9. From the unequally retarded control signals 11.1, uz and us, the desired scrambling signal '0 is obtained by forming modulation products of the intermediate signals in K6 and K8 and filtering out in each case one of the side bands in B6 to Be. In this manner, the relation between the scrambling signal '1) and the control signal u is very difficult to determine in attempting to unscramble the message by an unauthorized receiver.

Instead of a mutual modulation it is also possible to obtain a scrambling signal by superposition or by adding the unequally retarded signals 2L1, M2 and us.

As is understood, corresponding converting devices have to be provided at the receiving end in order to obtain intelligible signals.

" Various additional methods for producing scrambling and unscrambling signals from a given control signal transmitted from the transmitter to the receiver will suggest themselves to those skilled in the art for utilization in connection with the invention. Furthermore, the actual scrambling and unscrambling of the message may be effected in accordance with any suitable methand b2, 02, respectively, are

0d difiering from those shown for illustration. In all cases the characteristic features of the invention consist in the transmission of a control signal from the transmitter to the receiver and with conversion of the signal in a not easily determinable manner both at the transmitter and the receiver to obtain the scrambling or unscrambling signals proper, the latter serving to control the scrambling and unscrambling of the message, respectively.

I claim:

1. In a method of secret signaling, the steps of transmitting a variable control signal together with a message from a transmitting to a receiving station, equally converting said control signal 'at both said transmitting and receiving stations into scrambling and unscrambling signals, respectively, having predetermined complex characteristics, and utilizing the converted signals to control the scrambling nd unscrambling of said message, respectively.

2. In a method of secret signaling, the steps of deriving a variable control signal from the frequency band of a message to be transmitted, transmitting said control signal together with said message from a transmitting to a receiving station, equally converting said control signal at both said transmitting and receiving stations into scrambling and unscrambling signals, respectively, having predetermined complex characteristics, and utilizing the converted signals to control the scrambling and unscrambling of said message, respectively.

3. In a method of secret signaling, the steps of transmitting a continuously variable control signal together with a message from a transmitting to a receiving station, equally and adjustably converting said control signal at both said transmitting and receiving stations to obtain scrambling and unscrambling signals, respectively, having predetermined complex characteristics, and utilizing the converted signals to control the scrambling and unscrambling of said message, respectively.

4. In a method of secret signaling, the steps of transmitting a periodically varying control signal together with a message from a transmitting to a receiving station, equally varying the characteristics of said control signal at both said transmitting and receiving stations to produce converted signals having predetermined complex characteristics, and utilizing the converted signals to control the scrambling and unscrambling of said message, respectively.

5. In a method of secret signaling, the steps of transmitting a periodically varying complex control signal together with a message from a transmitting to a receiving station, equally varying the characteristics of said control signal at both said transmitting and receiving stations to produce converted signals having predetermined characteristics, and utilizing said converted signals to control the scrambling and unscrambling of said message, respectively.

6. In a secret signaling system comprising means for transmitting a periodically varying complex control signal comprising a band of component frequencies together with a message from a transmitting to a receiving station, means for equally dividing said control signal at both said transmitting and receiving stations into a plurality of frequency sub-bands, means for equally converting the characteristics of corresponding sub-bands of the transmitted and received control signals and for recombining the converted 7 sub-bands to produce variable scrambling and unscrambling signals at said transmitting and receiving station, and means for controlling the scrambling and unscrambling of said message by said scrambling and unscrambling signals, respectively.

7. In a secret signaling system comprising means for transmitting a periodically varying complex control signal comprising a band of component frequencies together with a message from a transmitting to a receiving station, means for equally dividing said control signal at both said transmitting and receiving stations into a plurality of frequency sub-bands, means for equally converting the frequency characteristics of corresponding sub-bands of the transmitted and received control signals and for recombining the converted sub-bands to produce variable scrambling and unscrambling signals, and means for controlling the scrambling and unscrambling of said message in accordance with said scrambling and unscrambling signals, respectively.

8.111 a secret signaling system comprising means for transmitting a periodically varying complex control signal comprising a band of component frequencies together with a message from a transmitting to a receiving station, means --for' equally dividing said control signal at both said transmitting and receiving stations into a plurality of frequency sub-bands, means for equally converting the amplitude characteristics 'of co r responding sub-bands of the transmitted and received control signals and for r combining the converted sub-bands to produce variable scramblingand unscrambling signals, and means for controlling the scrambling and unscrambling of said message in accordance with said scrambling and unscrambling signals, re- 's'p'ectively.

9; In a secret signaling system comprising means for transmitting 'a periodically varying complex control signal comprising a band of component frequencies together with a message from a transmitting to a receiving station, means for equally dividing said control signal at both said transmitting and receiving stations into a 13111- rality of frequency sub-bands, means for equally delaying the corresponding sub-bands of the transmitted and received control signals and for recombining the converted sub-bands to produce variable scrambling and unscrambling signals, and means for controlling the scrambling and unscrambling of said message in accordance with said scrambling and unscrambling signals, respectively.

10. In a secret signaling system comprising "means for transmitting a periodic control signal together with a message "from a transmitting to a receiving station, means for equally converting said control signal at both said transmitting and receiving stations to derive scrambling and unscrambling signals of predetermined complex characteristics, and further means for controlling the scrambling and unscrambling of said message in accordance with said scrambling and unscrambling signals, respectively.

11. In a secret signaling system comprising means for segregrati-ng a control signal from the energy of a message to be transmitted, means for transmitting said control signal together with said message from a transmitting to a receiving station, means for equally converting said control signal at both said transmitting and receiving stations to derive scrambling and unscrambling signals of predetermined complex characteristics,

and-further means for-controlling the scrambling and unscrambling of said message in accordance with said'scrambling and unscrambling signals, respectively. 7 r

'12, In a secret signaling system comprising means for producing a control signal by extracting fractional energy of predetermined characteristics from a complex frequency band of a message to be transmitted, means for transmitting said control signal together with said message from a transmitting to a receiving station, means 'for equally converting the control signal at both said transmitting and receiving stations to derive scrambling and unscrambling signals of predetermined complex characteristics, and further means for controlling scrambling and unscrambling of said message in accordance with said scrambling and unscrambling signals, respectively. v

13. In a secret signaling system comprising means for transmitting a complex periodically varying control signal together with a message from a transmitting to a receiving station, means for equally dividing said control signal at both said transmitting and receiving stations into a plurality of frequency sub-bands, means for differently changing the amplitude characteristics of the control signal sub-bands at both the transmitting and receiving stations and for recombining the changed sub-bands to produce scrambling and unscrambling signals, respectively,'the change of the control signal-sub-bands at the receiving station being equal to the change of the corresponding control signal sub-bands at the transmitting station, and means for controlling the scrambling and unscrambling of said message in accordance with saidjscrambling and unscrambling signals, respectively. V

14. In a secret signaling system comprising means for transmitting a complex periodically varying control signal together with a message from a transmitting to a receiving station, means for "equally dividing said control signal at both said transmitting and receiving stations into a plurality of frequency sub-bands, means for differently delaying the control signal sub-bands at both the transmitting and receiving stations and for recombining the delayed sub-bands to :produce scrambling and unscrambling signals,

respectively, the delays of the control signal subbands at the receiving station being equal to the delays of the corresponding control signal subbands at the transmitting station, and means for controlling the scrambling and unscrambling of said message in accordance with said scrambling and unscrambling signals, respectively.

15. 111. a 'secretsignaling system comprising means for transmitting a complex periodically varying control signal together with a message from a transmittingto a receiving station, means "for equally dividing said control signal at both said transmitting and receiving stations into a plurality of frequency sub-bands, means for differently and adjustably delaying the control signal sub=bands at both the transmitting and receivingstations and for recombining the delayed sub-bands to produce scrambling and unscrambling signals, respectively, the delays of the control signal sub-bands at the receiving station bein'g'equal to the delays of the corresponding control signal sub-bands at the transmitting station, and means for controlling the scrambling and unscrambling of said message in accordance with said scrambling and unscrambling signals,

respectively.

. V l 77 I V l I 16. In a secret signaling system comprising means for transmitting a complex periodically varying control signal together with a message from a transmitting to a receiving station, means for equally dividing said control signal at both said transmitting and receiving station into a plurality of frequency sub-bands, means for differently delaying the control signal sub-bands at both the transmitting and receiving stations and for recombining the delayed sub-bands by mutual intermodulation and filtering of a predetermined frequency band from the modulation product to produce scrambling and unscrambling signals, respectively, the delays of the control signal sub-bands and their mutual intermodulation and filtering at the receiving station being equal to the delays of the corresponding control signal sub-bands and their mutual intermodulation and filtering at the transmitting station, and means for controlling the scrambling and unscrambling of said message in accordance with said scrambling and unscrambling signals, respectively.

17. In a secret signaling system comprising means for transmitting a periodic control signal together with a message from a transmitting to a receiving station, means for equally changing a plurality of characteristics of said control sig nal at both said transmitting and receiving stations to derive scrambling and unscrambling signals of predetermined complex characteristics, and further means for controlling scrambling and unscrambling of said message in accordance with said scrambling and unscrambling signals, respectively.

18. In a secret signaling system comprising means for transmitting a periodic control signal with a message from a transmitting to a receiving station, equally changing a plurality of characteristics of said control signal at both said transmitting and receiving stations to derive scrambling and unscrambling signals of predeter' mined complex characteristics, and controlling scrambling and unscrambling of said message in accordance with said scrambling and unscrambling signals, respectively.

20. In a method of secret signaling, the steps of transmitting a periodic control signal together with a message from a transmitting to a receiving station, equally and adjustably changing a plurality of components of said control signal at both said transmitting and receiving stations to derive scrambling and unscrambling signals of predetermined complex characteristics, and controlling the scrambling and unscrambling of said message in accordance with said scrambling and unscrambling signals, respectively.

GUSTAV GUANELLA. 

